Preparation And Performance Study Of Long Afterglow Materials

Long afterglow phosphorescence?LAP?luminescent materials are referred to as Long-lasting phosphorescence?LLP?materials,which are also known as light-storing luminescent materials.It is a kind of material that absorbs energy such as visible light,ultraviolet light,X-ray and so on,and can persist luminescence after the excitation is stopped.Long afterglow phosphorescence materials have been widely used in various areas,including emergency lighting display,traffic signs,decoration,fabric printing and other weak light display fields,multidimensional optical memory and imaging storage,detection of high-energy rays such as UV,x-ray,-ray etc.Alkaline earth stannate has the advantages of stable crystal structure,excellent physical and chemical properties,safe and harmless,low-cost.This paper selects alkali earth stannates M₂SnO₄?M=Ca,Sr?as the host matrix.The novel rare earth-dopedM₂SnO₄?M=Ca,Sr?long persistent phosphorescence materials with red,green,yellow and white afterglow were sintered by high temperatue solid reaction in air atmosphere and vacuum at-mosphere respectively.The phases of samples were identified by X-ray powder dif-fraction?XRD?.The fluorescence properties of the synthesized samples were ana-lyzed by absorption spectrum,excitation spectrum and emission spectrum.The after-glow performance of the samples was characterized by the afterglow spectrum and the afterglow decay curve.The appropriate afterglow mechanism analysis was performed.The specific research contents and results of this paper mainly include the following aspects:1.When M₂SnO₄?M=Ca,Sr?is prepared by high temperature solid-state reaction,the CaCO₃ and SnO₂ preferentially form the unstable intermediate phase CaSnO₃,and the intermediate phase then reacts with CaO to form the stable target Ca₂SnO₄ phase.The suitable synthesized temperature is 1400°C for 4 h.The optimal luminescent properties of Sm³⁺ion doping concentration in the sample Ca₂SnO₄:xSm³⁺is x=0.001.The main emission peaks of the Ca_2-xSnO₄:xSm³⁺material are located at 610,619,654 nm,respectively belonging to ⁴G_5/2-⁶H_J?J=5/2,7/2,9/2?transitions of Sm³⁺.Photoluminescence measurement indicates that Ca₂SnO₄:Sm³⁺shows an orange-red emission with the CIE 1931 coordinates at?x=0.603,y=0.3951?and?x=0.5635,y=0.4358?.The afterglow mechanism of Ca₂SnO₄:Sm³⁺is analyzed in detail.The per-sistent luminescence after irradiated under low-energy light?about 365 nm?,occurs through the quantum tunneling process.This tunneling process needs not go through the conduction band and proceeds at a slow rate.So,it produces much weaker longpersistent luminesce.2.The new red long afterglow phosphorensce Ca_2-x-x SnO₄:xEu³⁺and yellow long afterglow phosphorensce Sr_2-xSnO₄:xEu³⁺were prepared by by high temperature sol-id-state method.The optimal Eu³⁺concentration is x=0.2 for the fluorescence.The CIE coordinates of the fluorescence emission spectrum were?x=0.6548,y=0.3449?,which located in the red region of the CIE 1931 chromaticity diagram.It is the de-pendence of the emission spectra and afterglow spectra of Ca_2-xSnO₄:xEu³⁺samples on the doped concentration of Eu³⁺ions,which indicated the ⁵D₀-⁷F₁ magnetic dipole transition of Eu³⁺plays a major role in the afterglow performance.Although the solu-bility of the lower Ca site is high for the Eu³⁺ion?x=0.2?,the solubility of the higher symmetry Sn site for the Eu³⁺ion is very low?x=0.001?.Because of the differences in crystal symmetry between tetragonal SrSnO₄ and orthorhombic Ca₂SnO₄,their lu-minescent colors are different.3.Several novel afterglow phosphorences were developed,such as red Ca₂SnO₄:Pr³⁺,green Ca₂SnO₄:Er³⁺,white Ca₂SnO₄:Dy³⁺.the long afterglow phos-phorensce host lattices and activators were expended.After the irradiation under 254nm,Ca_1.9993SnO₄:0.0007Pr³⁺emits reddish orange afterglow with CIE coordinates?x=0.6726,y=0.3271?in the CIE 1931 chromaticity diagram.The afterglow spectrum mainly consists of two peaks at 604,625 nm.The phosphorensce Ca₂SnO₄:Er³⁺emites green long-lasting emission.The afterglow spectrum peaks are mainly distrib-uted in 525,536,552,559 nm attributable to ²H_11/2–⁴I_15/2 of Er³⁺ions.When dopant concentration reaches x=0.005,the afterglow performance is best,with the chromatic-ity coordinates?x=0.2777,y=0.7042?yellow-green.The phosphorensce Ca₂SnO₄:Dy³⁺,emites intense white luminescence with the spectrum peaks consist of476,480,492 nm?blue?,561,573 nm?yellow?,and 667 nm?red?.When the concen-tration of Dy³⁺x=0.005,the afterglow performance is best.The calculated CIE 1931color space coordinate is?x=0.3347,y=0.3701?which located in the white light color space.4.The trap center of the long afterglow material comes mainly from auxiliary ac-tivator.Different auxiliary activator makes the luminescent phosphor have different trap level.It was found that the co-activated ions can significantly improve afterglow performance?brightness and decay life?without changing the afterglow color.The afterglow brightness of Ca_1.945SnO₄:0.005Sm³⁺,0.05La³⁺was 6 times higher than that of Ca_1.995SnO₄:0.005Sm³⁺.And the afterglow brightness of Ca₂SnO₄:Eu³⁺could be impoved as 4 times by co-doping with Gd.The co-doping of the co-activator produces more hole traps at the appropriate energy level,which favors the enhancement of af-terglow.5.The long afterglow phosphorensce Ca₂SnO₄:RE³⁺?RE=Pr,Sm,Er?were synthesized by high temperature solid state method in vacuum atmosphere.The vac-uum sintering process quenches the broad excitation band centered at 335 nm of Ca₂SnO₄,but does not cause any change in the emission spectrum.Comparing with the air-sintered sample,a significant enhancement in phosphorescence for the vacu-umsintered sample was observed.This improvement could be attributed to the in-crease of oxygen vacancies which act as the sensitizer and the electron traps for the effective energy transfer from Ca₂SnO₄ host to RE³⁺.The afterglow brightness of the synthesized Ca₂SnO₄:Eu³⁺,Ca₂SnO₄:Sm³⁺,Ca₂SnO₄:Er³⁺synthesized in the vacuum atmosphere were increased by 3.6,2,and 3 times,respectively.